Back pain caused by degenerative disc disease is associated with significant costs and patient morbidity. Although previous studies have thoroughly investigated the matrix of degenerated discs, few studies have investigated the subset of degenerated discs that are specifically painful. Detailed knowledge of how these properties in painful discs compare to those of nonpainful discs will provide guidelines for the development of tissue engineered treatment. The goal of the current dissertation is to characterize the matrix of the painful disc and investigate nucleus pulposus tissue engineering.
We characterized painful and nonpainful discs that were harvested from waste tissue of human surgical patients. The mechanical properties, matrix properties, and matrix synthesis of these tissues were measured using mechanical indentation, hydration, biochemistry, histology, and gene expression. Our data indicated that the painful annulus had altered gene and protein expression of proteoglycan and collagen, and consequent diminished mechanical properties. In contrast, the painful nucleus had elevated gene expression of decorin and higher energy dissipation than the nonpainful nucleus. Interestingly, gene expression data of several proteoglycans and collagens correlate with indentation and hydration properties.
In addition to characterizing the matrix properties of painful discs, we investigated the differentiation of human mesenchymal stem cells (MSCs) into nucleus pulposus cells for tissue engineering. Specifically, MSCs were seeded into a three-dimensional alginate scaffold, pretreated with growth factor, and stimulated with mechanical compression. The effect of compressive stimulation on cell differentiation was measured by gene expression of several chondrogenic markers, including aggrecan, collagen II, Sox9, collagen I, and collagen X. Our data indicate that growth factor treatment promotes production of chondrogenic matrix proteins, including proteoglycans and collagen II; however, compressive stimulation had no effect on gene markers of chondrogenic differentiation.
The results of this dissertation suggest that painful discs have diminished mechanical and matrix properties. Importantly, these diminished properties have previously been associated with pain mechanisms via disc hypermobility, stress concentrations, and reduced barriers to nerve infiltration. Although our investigation of MSC differentiation with compressive stimulation was inconclusive, our characterization of painful disc matrix may guide future attempts to regenerate painful degenerated discs.